A premature neonate develops neonatal tetany with hypocalcaemia. Lab findings: serum Ca2+ 1.4 mmol/L (low), phosphate 2.8 mmol/L (high), PTH low-normal, vitamin D normal. The MOST likely diagnosis is:

• A Neonatal hypocalcaemia due to transient relative hypoparathyroidism from maternal hyperparathyroidism ✓
• B Primary hypoparathyroidism due to DiGeorge syndrome
• C Hypomagnesaemia impairing PTH secretion and action
• D Vitamin D-dependent rickets type 1 (1-alpha hydroxylase deficiency)

Explanation

When maternal PTH is chronically elevated (primary or secondary hyperparathyroidism), transplacental calcium transfer is increased, suppressing fetal parathyroid gland development. At birth, when placental calcium supply ceases, the neonate's suppressed parathyroid glands cannot respond — causing transient hypocalcaemia with inappropriately low-normal PTH. DiGeorge syndrome would also present with hypocalcaemia but is associated with absent thymic shadow and cardiac defects. The high phosphate with hypocalcaemia points to impaired PTH secretion, not vitamin D deficiency.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.